The plants in Kinnaur district were shut down Sunday as the silt level in the river shot up following incessant rains.
"The silt level in the river is still alarmingly higher than the permissible limit," said Vijay Verma, deputy general manager of Sutlej Jal Vidyut Nigam Ltd (SJVNL), the company that owns and operates the 1,500 MW Nathpa Jhakri power project.
He said power generation cannot be resumed till the silt content comes down. Silt damages the power generators when water runs them. "Heavy rainfall in the catchment area is responsible for high silt," he added.
Jaypee Group's 1,000 MW Karcham Wangtoo Hydroelectric Project has also been shut.
However, its other 300 MW Baspa hydropower project, located upstream of the Karcham Wangtoo project, resumed generation Tuesday.
Official sources said the shutting down of the plants has created a power shortage in the northern states.
The plants supply electricity mainly to Punjab, Haryana, Chandigarh, Himachal Pradesh, Delhi, Jammu and Kashmir, Rajasthan, Uttar Pradesh and Uttarakhand.
The SJVNL, a joint venture between the centre and the state government, generates about 38 million units of power daily.